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But Roberts, who could win a fourth Wales cap against Denmark on Friday, says he has only seen Bielsa's softer side since breaking into the first-team at Elland Road.

'I haven't seen him blow up,' Roberts said. 'He was OK after Saturday (when Leeds lost 4-1 at West Brom). He always shakes everyone's hand when we come in from the pitch.

'It's always the same, win or lose. He was obviously not happy about Saturday, but that's the same in every team after a result like that.'

Roberts joined Leeds from West Brom for £2.5million in January but injuries kept him out of the first-team picture until Bielsa's arrival. The 19-year-old, however, has made a big impact since with three goals in seven league starts.

Bielsa — who is known as El Loco — is not as explosive behind the scenes as some would think

Those goals have helped Leeds into third place in the Sky Bet Championship table and has coincided with Roberts making his mark on the international scene.

'I started as a winger with him (Bielsa),' said Roberts. 'But he's seen me come away with Wales and play the number nine role.

'He's taught me a lot about runs in behind, staying up the pitch and making important movements. He's opened my eyes to another part of my game that maybe I didn't see as well before.

'He's got so much respect in the game and everyone at Leeds has bought into that culture.'

He has impressed during appearances for Leeds, scoring three goals in seven league starts

Roberts' breakthrough at Leeds has been replicated at international level under Wales boss Ryan Giggs.

He made his debut in September's Nations League victory over Republic of Ireland and his first start against the same opponents last month, a 1-0 win in Dublin.

Wales will top the group and secure promotion to the top tier of the Nations League by beating Denmark at the Cardiff City Stadium.

That has also resulted in Roberts getting more opportunities for Wales over recent months

'The confidence the manager has in me helps me on the pitch to do what I've been doing,' Roberts said. 'Over the last six months it's escalated quickly and took me by surprise.

'But I've been ready for every obstacle and just want to keep going and push on even more.

'I must admit I was star-struck when I first came into the squad and trained with Gareth (Bale) and Aaron (Ramsey).

'But you have to realise that they are your teammates and it's just great to observe them and learn from them.'